1. Field of the Invention
The present invention relates to a method, system, and program for managing calibration files and, in particular, selecting a calibration file matching output-appearance attributes associated with a print job to use to calibrate the print job.
2. Description of the Related Art
To print an image, the image is first scanned by an input device and transformed to a gray scale representation of the image. A gray scale image is comprised of a matrix of thousands of pixels such that each pixel has a color or shade of grey value indicating a color or shade of grey for the pixel. In a 256 color system, each pixel may have one of 256 different color or shade of grey values. After an image is scanned, the gray scale bit map produced by the scanner must be further processed into a bit map format that the printer can process. Because most printers only print a limited number of colors or either black or white, the gray scale image is converted, using a halftone process, into a bi-level or halftone image, where each bit map value indicates either black or white. Thus, a halftoning transformation is applied to the gray scale image to convert the gray scale representation of the image to a bi-level image. The halftoning transformation would use dithering, also referred to as screening, to simulate the shades of grey or colors in the gray scale image by varying the pattern of dots. Thus, the result of dithering is a bi-level bit or halftone map where each value indicates one of two colors—black or white, with the dithering used to simulate shades. Contone printers print a limited number of shades of a color or grey. Thus, a processed bit map for a contone printer may include a limited number of values for each bit map value, such as eight, and also use dithering to simulate additional shades of grey and color.
Many images are stored as variants of red, green, and blue, i.e., RGB system. However, printers use the colors cyan, magenta, yellow, and black to print, i.e. CMYK. When printing an image in an RGB format, such as an image displayed on the monitor, the RGB image is first transformed to a device dependent CMYK color space that corresponds to the RGB space. However, different printers produce varying output given the same CMYK input color space. The ability of a printer to reproduce an input image may be affected by many printing variables, such as the model of the printer, the age of the printer, the paper, toner, and environmental variables, such as temperature and pressure. All these variables affect how a printer produces an image from the CMYK input color space.
To account for variables, a printer is calibrated. Calibration occurs by having the subject printer print patches of colors having known color values. A device referred to as a densitometer than measures the printed color values. The printed color values are than compared to the actual value of the colors maintained for the patches. Mathematical interpolation is used to generate a calibration curve which relates the actual printer measured output to the input patch of colors. This calibration curve provides a mapping from input color values, in a device independent CMYK space, to printer CMYK values that will produce the desired colors. Thus, the calibration curve maps the target or colors of the actual gray scale image to the printer, device dependent, CMYK color space. After the calibration curve is applied to adjust the input color or grayscale values, a halftone and dithering algorithms are applied to convert the calibrated gray scale image into a bi-level matrix where each pixel has only one of two values, or for a contone printer one of only a few values.
In current printing systems, the printer or server managing printer operations will include some factory provided calibration curves to apply to an input CMYK color space. Printer manufactures typically provide a calibration curve file for a printer model. This factory printer model calibration curve is then used for any output for that model printer, regardless of the presence of additional printing variables that may not have been present when the calibration curve was generated at the factory. In the publishing environment where print quality is essential, the publisher may generate specific calibration curves for a printer operation as the factory provided calibration curves may not account for numerous printing variables under which the publisher is printing, such as the age of the printer, paper, toner, temperature, etc. However, after generating such printer specific calibration curves for use with that printer, the publisher may discard the calibration curve files or save the new calibration curve in place of the factory provided calibration level. Large publishers could generate numerous calibration curves during the course of printing different publications. After using the calibration curves for the specific publishing job, they are then usually discarded or maintained by the publisher to manually select again when submitting a print job.
There is a need in the art for a system for effectively and automatically managing user generated calibration files.